unicode, cyrillic displayed problems

I’ve got a problem in my 3languages site, when i write in russian ciryllic the characters turns into question marks (????).

I found online a potential solution that is:

https://www.ads-software.com/support/topic/cyrillic-text-turns-into-in-blog-posts-and-comments?replies=4

Are you getting ???? errors instead of Cyrillic when typing Russian? This can be quite frustrating, but not too hard once you know the code to fix. Took me about half a day to figure out, so hopefully, this will save someone a lot of time. Make sure to save your original wp-config.php files in case the need arises to re-install it.
If you are on a windows server you will need to change your wp-config.php file as follows.
define(’DB_CHARSET’, ‘utf8′);
to
define(’DB_CHARSET’, ‘windows-1251′);
or
define(’DB_CHARSET’, ‘windows1251′);
If you are on a linux server, such as I, you will need to change your wp-config.php file as follows.
define(’DB_CHARSET’, ‘utf8′);
define(’DB_COLLATE’, ”);
to
//define(’DB_CHARSET’, ‘utf8′);
//define(’DB_COLLATE’, ”);

I’m a linux host user so i tried the linux solution (and also the windows one after) but it’s not working.

Was it the right solution or what should i do now?
Thanks in advance